The subject invention is directed toward the art of work holders and, more particularly, to a rigid collet device for holding cylindrical workpieces.
The invention is especially suited for use as a tube clamp unit in an orbiting head tube welder and will be described with particular reference thereto; however, the invention is capable of broader application and could be incorporated in a wide variety of work holders and clamping units for different types of cylindrical work pieces.
In U.S. Pat. No. 4,379,215, issued Apr. 5, 1983, for "Orbital Cassette Welding Head", there is disclosed an apparatus for welding abutting tube sections. The apparatus includes an orbital welding head unit and a separate U-shaped tube clamp unit which holds the tube sections to be welded in abutting aligned relationship during the orbiting of the weld head about the tube ends. The tube clamp unit uses rigid collets to hold the tube sections in alignment during the welding operation.
The use of rigid collets for holding the tubing during the welding operation is much preferred as compared to split and/or adjustable collets or similar holding devices. The reason for this is that during the welding operation, thermal stresses tend to cause the tubing to move creating misalignment between the two sections. The movement is greater and/or more likely to happen with the split collets and the adjustable collets or holders. With respect to the solid or rigid collets, however, there are problems in assuring that tubing throughout the range of standard commercial tolerances can be held properly. That is, a typical commercially available tubing used for fluid systems and the like, has, for example, a nominal outside diameter of 0.50 inches which varies .+-.0.005 inches. It has been difficult to compensate for the diameter variations which result from the tolerance variations and, at times, it has been difficult to properly hold the tubing during the welding operation.
As can be appreciated from the foregoing, the need persists for a collet design which allows the maintenance of the rigid collet form while providing compensation for the outer diameter variations which result from tolerance variations.